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Hello, I have been forging and fabricating for 10 years, but haven't really done any heat treating other than annealing and case hardening when I first started. It has come to my attention that there are some terms that I just don't know or was never taught. These are magnetic and non-magnetic heats and normalising. Would be thankful if someone could enlighten me. Thanks and forgive my ignorance!

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You know how to anneal, heat above critical and cool very slowly, say in a bucket of fluffy wood ash. Normalization is very similar. You heat above critical and cool in still air for many steels. It serves a similar purpose in relieving stress, and rendering a softer state, but not as soft as possible.

Magnetic: a magnet is attracted to it
non-magnetic: a magnet is not attracted to it. For many steels non-magnetic and critical happen at about the same temperature. Get a ceramic doughnut magnet, about $3 for 5 at Radio Shack, hang from a thin copper wire. If the magnet is attracted to the metal, it is magnetic, if the magnet swings naturally it is non-magnetic.

This temperature is also called the Curie point.
http://en.wikipedia.org/wiki/Curie_temperature

Phil

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magnetic heat is when the steel is heated it is still magnetic.

non-magnetic heat is when heated to a high enough temp. steel loses its magnetic properties, but only while it is at that high temp. once it drops in temp it regains its magnetic properties.

normalizing...it heating the metal to it's critical temp and then allowing it to cool on its own slowly. this relieves the stresses of forging. when done prior to hardening, normalizig helps relieve the stresses that might lead to spontenious cracking when quenching hot steel.

this is my understnding of these terms. If i am wrong please someone correct me.

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I may not get all the technical right but steel below a certain temp is magnetic I think somewhere in the dull red area it looses its ability to have a magnet stick to it. That is the magnetic and non magnetic, I do not remember just now about upper and lower transformation temperatures but someone with more knowledge than I will chime in soon. I think normalizing is heating the steel above a certain temp and holing it for a length of time. Depends on the alloy of steel as to what time and temp. Please add or correct as needed since I do not do this often enough to know for sure.
Rob

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I think there's more to normalizing than some of the other posters have indicated. Normalizing is generally accomplished by heating steel to slightly above critical temperature and then allowing it to cool to below critical, but I think the effects of this process go beyond simple stress relief. It's my understanding that repeated normalizing cycles have the effect of refining the grain size of the steel, producing small grain size and greater toughness. I'm told this occurs because new pearlite grains form on the boundaries of the old Austinite grains as the steel cools. I think you can get the same result with repeated quenching/hardening cycles, but there is obviously a greater risk of damage to the steel with that approach. Many knife makers will do three or four normalization cycles after forging but prior to hardening in order to improve blade performance and resistance to breakage. (Cracks and breaks tend to propagate along grain boundaries, so, as a general rule, the smaller the grain size, the tougher the metal.)

If you want to understand this stuff better, the book "Steel Metallurgy for the Non-Metallurgist" by J. D. Verhoeven is absolutely superb. (Here it is on Amazon, but you can probably find it used for less: http://www.amazon.com/Steel-Metallurgy-Non-Metallurgist-J-Verhoeven/dp/0871708582/ )

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  • 1 month later...

For plain carbon, 0.35% through 1.3% carbon steel, normalizing is recommended rather than annealing by present day metallurgists, because with annealing, you "retain large carbides." which are undesirable.

With some alloy steels, you cannot normalize, because they are air hardening.

http://www.turleyforge.com Granddaddy of Blacksmith Schools

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  • 1 month later...

I know that this thread has been up here for a while, but I have to respond to this one. I am a retired tool and diemaker and have heat treated a variety of steels for over 30 years.

What most people refer to as tempering really isn't. There is a temperature range of generally about 75-100 degrees ie 1800-1875 for a lot of steels where the steel has to be heated to in order to harden fully. Once it is quenched (air, oil or water) and the temperature drops quickly enough it will be at its maximum hardness. This maximum hardness material, however, is very brittle due to the stresses caused by the quenching and once it has reached room temperature must be reheated and "soaked" at a temperature which is held for a number of hours depending on how hard you want the tool to be for final use. Generally any tool steel that reaches a quench hardness of 60 Rockwell on the "C" scale will be "Tempered" to a few points below this hardness. The tempering or normalizing relieves the shock caused by the quenching and makes the crystaline structure of the steel consistent and reduces the tendency to fracture during use. Most air hardening tool steels like A-2 need to be held at 300-400 degrees for two hours and then be air cooled and have the process repeated again to adequately stabilize the material. If the material is over an inch thick you have to add another hour for every additional inch thickness. Crucible Steel Company has an excellent guide for the heat treatment of steels.

I would suggest unless you want to spend the money to acquire a digital controlled oven and do your own heat treating, that any critical part you want to harden send it to a commercial heat treating company. They generally will heat treat based on a minimum fee for a certain number of pounds of materiel sent in for the same specification of hardness and tempering. They will have the capability of vacuum heat treating and doing an inert gas quench on any items you do not want scale on.

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I know that this thread has been up here for a while, but I have to respond to this one. I am a retired tool and diemaker and have heat treated a variety of steels for over 30 years.

What most people refer to as tempering really isn't. There is a temperature range of generally about 75-100 degrees ie 1800-1875 for a lot of steels where the steel has to be heated to in order to harden fully.

...


I think you are a little hot, since most steel specifications I have looked at call out 1500F or there about. I am sure there are some steel that is up in that range, but that is not typical.

I recommend that anybody look up the data sheet on the steel you are using before heat treat, and often before forging even. The forging temperature range and the heat treat temperatures are spelled out plainly. Google will find the information quickly I search the steel specification for example "4140 specifications" provides a first return of

http://www.metalsuppliersonline.com/research/property/metals/25.asp

It specifies hardening as quench from 1550F after normalizing. Instructions for normalizing are also given.

Yes, if the instructions are requiring complex or very long soaks you may be best served sending the part out for heat treat if you do not have a controlled oven capable of the specified temperatures.

Naturally there are exceptions that experience (yours or others) can allow high quality heat treat without specialized equipment on certain alloys (h13 was discussed to this effect for punches and thin regular sections)

Phil
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